1. Field of the Invention
This invention relates generally to a photographic exposure control system and, more particularly, to a photographic exposure control system where the scene light is integrated during the exposure to a level determined as a function of a pre-exposure ambient scene light detection.
2. Description of the Prior Art
Automatic light responsive exposure control systems as well known in the photographic arts and have been long used to control the duration of a photographic exposure. Such exposure control systems are generally utilized to control a shutter blade assembly which is movable along a predetermined path between a first position precluding scene light from reaching a film plane and a second position defining a maximum size aperture thereby defining a progression of gradually increasing aperture sizes. It is often desirable to alter the operating characteristics of an exposure control system when used in conjunctionn with a source of artificial illumination as is more fully disclosed in U.S. Pat. No. 3,200,723, entitled "Shutter Timing Apparatus", by J. M. Topaz, issued Aug. 17, 1965. The operating characteristics of the exposure control system of Topaz are changed during a flash mode of operation to reduce exposure errors which would otherwise occur as a result of the exposure control system being calibrated to operate properly under ambient conditions when the scene illumination is of substantially constant intensity. Thus, when the exposure duration is controlled by a light integrating control circuit, selectively operable means are provided to reduce the amount of light required to trigger the circuit to cause termination of the exposure thereby reducing or eliminating errors in the amount of light which is allowed to impinge upon the film where the scene is illuminated by photoflash apparatus.
Apart from the obvious difficulties in reconciling ambient and flash exposure control resulting in differences between the uniform light intensity encountered during ambient mode operation and the varying light intensity encountered during flash mode operation, other difficulties arise as a result of the operational changes in the shutter assembly between ambient and flash operation. For instance, in a two-bladed shutter assembly of the scanning type, the command trigger signal from the light integrating control circuit to terminate the exposure interval is generally received while the shutter blade elements are moving in a direction of progressively increasing effective aperture size. Thus, the forward momentum of the shutter assembly must be overcome before the blades can start to return to their closed position. Hence, a considerable overshoot is experienced where the effective aperture defined by the shutter assembly primary apertures increases beyond its value at the time that the command trigger signal is received from the light integrating circuit. Such an overshoot in the effective aperture defined by the shutter blade elements may be easily anticipated in a well-known manner by configuring the photocell sweep apertures to move ahead of the shutter blade primary apertures. However, in the flash mode of operation where a source of artificial illumination is utilized, the shutter blade elements generally reach their maximum effective aperture defining position as determined by the follow focus system prior to receipt of the command signal to terminate the exposure interval. Hence, the shutter blade elements are already at rest at the follow focus setting when the command signal to terminate the exposure interval is received and thus the shutter blade elements do not overshoot their aperture defining position at the time of receipt of the command signal. Hence, the built-in anticipation for the ambient mode of operation becomes incompatible with the flash mode of operation to provide an adequate film exposure.
In photographic camera systems wherein a detachable source of artificial illumination such as a flash bulb is utilized, the difficulty has been solved in a manner as is fully described in U.S. Pat. No. 4,008,481, entitled "Exposure Control System with Separate Flash and Ambient Trigger Levels", by George D. Whiteside, issued Feb. 15, 1977, in common assignment herewith wherein the trigger level to which the scene light is integrated during the exposure interval is varied as a direct function of the insertion or with removal of the flash array from the camera apparatus. However, in newer photographic camera systems wherein an electronic flash may be an integral part of the photographic camera apparatus, it may be undesirable to require the photographer to actuate a button or like device just to vary the exposure level at which the shutter blades are commanded to close particularly where it is anticipated that the strobe may be utilized both under conditions of low ambient scene light intensity to provide the major portion of the scene illumination and under conditions of high ambient scene light intensity where the strobe may be utilized only to provide fill in flash in order to highlight shadows. In addition, it may become desirable to provide a plurality of different trigger levels by which to command the shutter blades to close in accordance with a predetermined exposure program.
Therefore, it is a primary object of this invention to provide an exposure control system for controlling the duration of an exposure interval as a predetermined function of both the ambient scene light detected prior to the exposure interval and the scene light detected during the photographic exposure interval in correspondence with the exposure of the film.
It is a further object of this invention to provide an exposure control system wherein the photographic exposure interval is terminated as a predetermined function of the scene light detected during the exposure interval wherein at least one parameter of the predetermined function is varied as another function of ambient scene light detected prior to the exposure.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplifed in the following detailed disclosure.